infection and response

• Types of Pathogen


  • Bacteria
  • Viruses
  • Protists
  • Fungi
• Bacteria


  Very small living cells that can reproduce rapidly inside the body and produce toxins that damage cells
• Viruses


  Not cells, much smaller than bacteria, can reproduce rapidly inside cells and cause cell damage when the cell bursts
• Protists


  Single-celled eukaryotes, some are parasites that can be transferred by vectors
• Fungi


  Can be single-celled or have a body made of thread-like hyphae that can penetrate skin and plants, produce spores that can spread
• Ways pathogens can be spread

  • Water
  • Air
  • Direct contact
• Measles is a viral disease spread by droplets from an infected person's sneeze or cough
• Measles can lead to serious complications like pneumonia or encephalitis
• Most people are vaccinated against measles when young
• HIV is spread by sexual contact or sharing needles, it attacks immune cells and can lead to AIDS if untreated
• Tobacco mosaic virus (TMV) is a virus that affects many plant species like tomatoes, causing discolouration and reduced growth
• Rose black spot is a fungus that causes purple/black spots on rose leaves, reducing photosynthesis and plant growth
• Malaria is caused by a protist, part of its life cycle is in mosquitoes which act as vectors to infect other animals
• Salmonella is a type of bacteria that causes food poisoning, can be spread by contaminated food like undercooked chicken
• Gonorrhoea is a sexually transmitted bacterial disease, originally treated with penicillin but now has antibiotic resistant strains
• Ways to reduce/prevent disease spread

  • Being hygienic
  • Destroying vectors
  • Isolating infected individuals
  • Vaccination
• Human body defences


  • Skin acts as barrier, secretes antimicrobial substances
  • Nose and airways trap particles
  • Stomach acid kills pathogens
• Immune system attacks pathogens that make it into the body
• Human body's defence system

  • Acts as a barrier to pathogens
  • Secretes antimicrobial substances that kill pathogens
  • Traps particles that could contain pathogens in nose and breathing passages
  • Stomach produces hydrochloric acid to kill pathogens
• Immune system's attack on pathogens

  1. Consuming them (phagocytosis)

  2. Producing antibodies

  3. Producing antitoxins
• Antibodies


  Proteins produced by white blood cells to lock onto and destroy invading pathogens
• Vaccination involves injecting small amounts of dead or inactive pathogens to cause the body to produce antibodies against them
• If a large percentage of the population is vaccinated

  Big outbreaks of disease (epidemics) can be prevented
• Pros of vaccination


  • Helped control many communicable diseases
  • Can prevent epidemics if a large percentage of population is vaccinated
• Cons of vaccination


  • Vaccines don't always work
  • Can sometimes have bad reactions
• Symptom-relieving drugs


  Relieve pain and symptoms but don't tackle the underlying cause or kill pathogens
• Antibiotics


  Kill or prevent the growth of bacteria causing the problem without killing the body's own cells
• Antibiotics don't destroy viruses
• The use of antibiotics has greatly reduced the number of deaths from communicable diseases caused by bacteria
• Bacteria becoming resistant to antibiotics

  1. Mutations cause resistance

  2. Resistant strains survive and reproduce

  3. Resistant strain can cause serious infection that can't be treated
• To slow down antibiotic resistance, doctors should avoid over-prescribing and patients should finish the full course of antibiotics
• Plant-derived drugs


  Plants produce chemicals to defend themselves, some of which can be used as drugs
• Microorganism-derived drugs


  • Penicillin from Penicillium notatum mould
• Drugs are now synthesised by chemists in labs, but the process may still start with a chemical extracted from a plant
• Developing Drugs


  1. Preclinical testing on human cells and tissues

  2. Preclinical testing on live animals

  3. Clinical trials on healthy volunteers

  4. Clinical trials on patients

  5. Peer review
• Preclinical testing on animals


  • Tests efficacy, toxicity, and optimal dosage
  • Required to test on two different mammals
• Clinical trials


  • Healthy volunteers test for side effects
  • Patients test for effectiveness
  • Randomised, double-blind, placebo-controlled
• Peer review helps prevent false claims
• Monoclonal antibodies


  Identical antibodies produced from a single clone of a B-lymphocyte
• Producing monoclonal antibodies


  1. Fuse B-lymphocyte with tumour cell to create hybridoma

  2. Clone hybridoma to produce identical cells

  3. Collect and purify antibodies